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What is a SIM only deal?

A SIM only deal refers to a contract that gets you an allowance of data, calls and texs for a monthly charge. The key difference from pay-monthly phone deals is that with SIM only deals, you're not paying for a phone. All you're paying for is the SIM and the allowances.

It's precisely because SIM only deals don't include a phone that they're usually a lot cheaper than standard mobile phone monthly contracts.

There are a number of types of SIM card. A standard SIM, Micro SIM and Nano SIM, all of which are different sizes. In general newer phones take the smaller Micro SIMs, while the newest phones accept Nano SIMs.

All three types of SIM card store the same information: that is, your phone number and call plan. It's only once you've inserted a SIM that you're able to use a mobile phone network.

Once a SIM card has been activated it is permanently locked to the particular network, though not locked to a particular phone. That means you can easily change mobile phone handsets but keep your phone number, your friends’ phone numbers and any saved messages or photos.

Want a phone-and-tariff contract instead? Take a look at some of the best on the market at our dedicated comparison page.

Why choose a SIM only deal?

If you're out of contract and happy with the phone you've got and don't want to upgrade to a newer model, it's smart to switch to a SIM only deal.

Otherwise, your network will continue to charge you the same monthly premium as when you were still paying for your handset. So going SIM only is a very good way to cut your outgoings and save some money.

More and more people are also opting to buy their phone outright and off-contract, then signing up for SIM only deal for data, minutes and texts. This can work out much cheaper than a standard phone contract.

But, of course, the catch is that you'll need hundreds of pounds to hand to be able to buy a smartphone outright if you don't already have one.

How much data should I look for in a SIM only deal?

That depends on how heavily you use your phone. For what it's worth, the average Briton gets through about 2GB-3GB per month.

That'll be fine for general usage. Think: checking your email, browsing the internet and social media sites.

But if you stream video or music heavily, you're going to need substantially more.

The smartest and best way to check you're choosing a SIM only deal with enough data is to open up your network app on your phone.

Here, you'll find a month-by-month breakdown of exactly how much data you've been using.

Use this as a guide when picking a SIM only deal and you won't go too far wrong. Unless, of course, you're planning to start using your phone a lot more in future.

How can I tell if my phone is unlocked and will accept another network's SIM?

Whether your phone is locked to your network depends on the network you're with and even on which handset you've got and which plan you bought it on.

For instance, all phones bought on EE and Vodafone are locked to their networks. So if you want to use another network's SIM, you'll first need to unlock your handset.

Conversely, when it comes to O2 phones sold on pay monthly plans, only some are unlocked. But if you got a pay-as-you-go phone from O2, all models are unlocked.

If you're with Three, the good news is that all phones they sell are unlocked. That applies irrespective of the model you own, the plan you bought it on or whether you bought it on pay monthly contract or pay as you go.

All sounds complicated, right? Agreed. But the good news is that there's a simple to check for sure whether your phone is unlocked.

All you need to do is to remove your existing SIM and insert another network SIM in your phone. You could borrow a friend's or family member's just to test it.

In the event that your phone accepts the SIM and you've got a mobile-phone signal, your phone is unlocked and you won't need to get it unlocked.

If there's no signal, your phone is locked. If that's the case, you'll have to call your network to ask them to unlock your smartphone and may have to pay a charge.

My phone is unlocked. What's my next move?

That's good news. That means you're good to go. The next step is to find a SIM only deal that suits you.

The best way to do is that by using the uSwitch comparison tables above. For some guidance as to which network to choose, take a look at all networks that picked up prizes at the 2019 uSwitch awards in the section below.

I've found a SIM only deal with another network. What do I do next?

The next step is to check that you’re not still under contract and are free to switch. The best way to do this to ring your network.

Once you’ve established that you are, sign up for for the SIM only deal you've chosen. Your SIM card should arrive within two days.

In the meantime, ring or email your network to tell them you’d like to leave. If your phone is locked, you'll also need to ask them to unlock your phone.

You may find you're encouraged to stay by their customer retentions department. If you are it's important that you're firm with them and insist that you're determined to switch.

A charge may apply for unlocking your phone. But this will only be between £15-£20. Once the phone is unlocked you can insert your new SIM and you're all set.

If you want to keep your number, make sure you also ask your current network for a PAC code (Porting Authorisation Code) when you notify them you’d like to leave. We’ll look at how you use your PAC code more closely in the section below.

Will a SIM only deal improve my credit rating?

Being accepted for 12-month SIM only deal can indeed improve your credit rating. That's because you're entering a contract and committing to paying for your monthly allowances on time every month.

By keeping your part of the bargain, you're showing potential lenders that you're trustworthy and a good bet for credit.

But be wary. If you miss your monthly payments, you risk damaging your credit score. If you think that making your payments might be a problem, it's probably wise to opt for a one-month SIM only deal, which will leave you free to cancel or downgrade your contract if money is tight.

Can I trust smaller, less well known networks? Is the service as good?

Although the likes of giffgaff and the people's operator aren't as instantly recognisable as high-street names such as Three, EE and Tesco Mobile, they're brands you can trust.

giffgaff, for instance, has won a slew of consumer awards, including Best Value for Money Pay Monthly from uSwitch.

In fact, many smaller networks offer market-leading call rates, so can work out cheaper.

You'll also find that there's no difference in call quality and mobile internet coverage with smaller providers.

That's because their service is based on larger providers' network infrastructure, which these smaller networks pay a fee to use.

Where you may find a difference compared with the larger networks is in customer support, however.

In order to keep prices low, some smaller networks don't operate a call centre and offer online support only.

If you choose smaller networks you also shouldn't expect enticing customer incentives, such as O2's Freebies or movie downloads with EE.

But you may decide that you don't want or need those and that a good service and cheap rates are your priority.

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